Operation of a battery system is dynamic and performance of a battery system varies significantly with age. The capacity of a battery degrades over the life of the battery. Over-charging and over-depleting may accelerate the degradation of battery capacity. Accordingly, control systems may be utilized in order to prevent over-charging and over-depletion to improve the lifespan of the battery system. In addition, the capacity of a battery may be affected by temperature and other operating conditions.
The capacity of a battery system included in an electric vehicle (“EV”) and plug-in hybrid electric vehicle (“PHEV”) may constrain the range of the vehicle. A battery system's SOH is a qualitative measure of a battery's ability to store and deliver electrical energy, while a battery system's state of charge (SOC) is a measure of electrical energy stored in the battery. Battery diagnostic and prognostic methods may be used to maintain proper battery operation and to provide a user with an indication of when the battery will become depleted. Battery diagnostics may track the degradation of battery's performance to estimate battery SOH and may track the SOC.
Control systems for estimating parameters of a battery system may incorporate algorithms such as the Kalman filter design, the classic least square design, and the extended Kalman filter design. Such systems, however, may not be suitable for some applications based on the time needed to estimate battery parameters, difficulty of such designs in adapting to changes resulting from battery age, battery variations, and operating conditions (e.g. temperature and SOC). Further, such systems typically estimate either battery states or battery parameters, but may not allow for concurrent estimation of both battery states and battery parameters. Finally, such systems may have difficulty recovering from an inaccurate estimation or measurement of an initial SOC or a battery capacity.